Guitars/basses with 2 necks are already known. The double necks give music performers dual sound capabilities and simultaneously allow them to have a double role during the musical performance. The double neck guitars/basses are mainly intended for live performance. E.g. when a musician while playing a live track does not have the time to leave the twelve-string guitar and catch the six-string, because this would mean to stop playing at all for at least some seconds. On the contrary, when playing an instrument with 2 necks, the change from one neck to another is almost instantaneous, taking imperceptible time. However the instruments with double necks apart from their increased cost, they have also a very limited use, only for specific circumstances of live music. This is why in the majority of the musical activities of most guitarists/bassists standard single neck instruments are used, which musicians always primarily own. Thus, for any guitarist/bassist buying an instrument with double neck is a high extra cost for an instrument probably not often needed.